Field of the Invention
The invention relates to a method of controlling or regulating the vertical position of piled or stacked sheets, more particularly, in a feeder of a sheet-processing machine, which includes determining the vertical position of the sheet resting on the top of the sheet pile, at the leading edge thereof and at the trailing edge thereof and, depending upon the vertical position of the leading edge and the trailing edge, respectively, moving at least one lifting element associated with the sheet trailing edge in the vertical direction.
The published German Patent Application DE 196 20 937 A1 reveals a method of the type mentioned hereinbefore, wherein the pile height, i.e., the vertical position of the sheet resting on the top of the sheet pile, is determined with the aid of sensors, a first sensor being associated with the pile leading edge, and determining thereat the information as to the height of the pile leading edge relative to a forwarding flap or an infeed roller on a feeder table, and a second sensor being applied to a lifting element associated with the pile trailing edge and furnishing information about the vertical position of the pile trailing edge relative to the lifting element, which is vertically adjustable by a motor. Because it is difficult to register the pile top edge at the leading edge, in particular, in the case of overlapping or imbricated feeders, because of the sheet delivery sequence and the great entrainment of air, wide variability of the measurement results often occurs. The direct use of the signal for controlling the lifting of the pile, and the subsequent control of the height of the lifting element based upon the information determined by the second sensor therefore leads to a poor, unstable control loop, wherein the correct vertical position of the sheets arranged under the lifting element can very often barely be assured. The pile height determined at the leading edge is often also too inaccurate if the pile height at the leading edge changes considerably and abruptly, as happens, for example, in the course of non-stop operation during the withdrawal of pile rakes and bars, respectively, arranged between the piled or stacked sheets.
It is accordingly an object of the invention to provide a method of controlling or regulating the vertical position of piled or stacked sheets, which does not have these drawbacks or disadvantages.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of controlling or regulating the vertical position of piled or stacked sheets, including determining at the leading edge and at the trailing edge, respectively, of the sheet resting on the top of the sheet pile, the vertical position of the sheet and, depending upon the vertical position of the leading edge and the trailing edge, respectively, moving in the vertical direction at least one lifting element associated with the sheet trailing edge, which comprises, displacing the sheet pile and the lifting element, respectively, a given distance in the vertical direction, when a large discrepancy is found between the vertical position at the leading edge and a nominal value.
In accordance with another mode, the method invention includes, when a small discrepancy is found between the vertical position at the leading edge and the nominal value, displacing only the lifting element in the vertical direction.
In accordance with a further mode of the method invention, the displacement of the lifting element in the vertical direction is relatively slow.
In accordance with an added mode, the method invention includes, when a large discrepancy is found between the vertical position at the trailing edge and the nominal value, displacing only the lifting element a given distance in the vertical direction.
In accordance with an additional mode of the method invention, the displacement of the lifting element is relatively quick.
In accordance with yet another mode, the method invention includes, when a small discrepancy is found between the vertical position at the trailing edge and the nominal value, displacing only the sheet pile a given distance in the vertical direction.
In accordance with yet a further mode, the method invention includes, when a small discrepancy is found between the vertical position at the trailing edge and the nominal value, displacing only the sheet pile continuously in the vertical direction.
In accordance with yet an added mode of the method invention, the nominal value of the vertical position at the trailing edge has a range of tolerance which is narrower than the range of tolerance of the nominal value of the vertical position at the leading edge.
In accordance with a concomitant mode, the method invention includes performing the steps thereof in a feeder of a sheet-processing machine.
In order to achieve the stated object of the invention, a method is proposed which can be used to control or regulate the vertical position of piled sheets in the feeder of a sheet-processing machine, such as a sheet-fed rotary printing machine, for example, the vertical position of the sheet resting on the top of the sheet pile is determined at the leading edge and at the trailing edge thereof. Depending upon the leading-edge vertical position and the trailing-edge vertical position, the sheet pile and at least one lifting element, respectively, associated with the sheet trailing edge is displaced accordingly in the vertical direction. The method is distinguished by the fact that in the event of a large discrepancy between the vertical position at the leading edge and a nominal or desired value, the sheet pile and the lifting element are displaced simultaneously or virtually simultaneously, respectively, a given or specific distance, in the vertical direction. As a result of the synchronous or virtually synchronous displacement of the sheet pile and of the lifting element, in particular large vertical discrepancies at the pile leading edge can be compensated for quickly, it being possible at the same time to prevent excessively large vertical discrepancies from the nominal value occurring from time to time at the trailing edge. Very narrow tolerances are preferably maintained or complied with at the sheet/pile trailing edge, in order to be able to assure reliable sheet separation.
In an advantageous embodiment of the method, in the event of a small discrepancy between the vertical position at the leading edge and the nominal or desired value, only the lifting element is displaced in the vertical direction. This is preferably performed only at a low speed. The displacement of the lifting element is preferably performed continuously until the nominal or desired value is reached again, or else cyclically, i.e., the lifting element is respectively moved vertically a given or specific distance. The vertical edge of the pile leading edge is therefore evaluated merely as a trend which is used for moving the lifting element vertically over a relatively great time, and therefore slowly, in such a way that the pile leading edge remains within the range of tolerance thereof.
In a preferred embodiment of the method, in the event of a large discrepancy between the vertical position at the trailing edge and a nominal or desired value, only the lifting element is displaced a given or specific amount in the vertical direction. This is preferably performed relatively quickly, i.e., at an appropriately high speed. Because of the low mass of the lifting element, it is therefore possible to react very quickly to a change in the vertical position of the trailing edge, and the lifting element can be tracked appropriately, so that in this case precise sheet separation can be assured.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as a method of controlling or regulating the vertical position of piled or stacked sheets, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: